Conventional power conversion systems generally use a power switching in constant voltage or a constant current mode. In a power conversion system, switch element on the primary winding of a transformer is turned on or off periodically producing a current flowing through the primary winding of the transformer, thus the energy at the primary side is transferred to the secondary side, and the AC current generated on a secondary winding is rectified and filtered while passing through an injection diode and a capacitor and converted into a direct current supplied to the load. However, the prior art is facing a problem in accurate evaluation of the output current provided to the load, especially in a Continuous Conduction Mode (CCM) and a Discontinuous Conduction Mode (DCM). Furthermore, the prior art is facing a problem in setting an output current basis to decide whether a flyback voltage converter accesses into an overload condition.